Cam follower device

ABSTRACT

A cam follower device includes a pair of plate-shaped rocker arms  17  parallel mutually, a support shaft  7   a  fixed in support holes  8   a   , 8   a  at one end portions of the rocker arms  17  at both end portions and a tappet roller  9  supported rotatably around a circumference of an intermediate portion of the support shaft  7   a . When the cam follower device is built in a valve train, rotary motion of a cam  2  provided on a camshaft is transmitted to valve elements  12  constituting two inlet (or exhaust) valves by the tappet roller  9  and the pair of rocker arms  17  so as to reciprocate the two valve elements  12  axially. By this configuration, the number of components in a valve train of an engine, in which a number of at least one of inlet and exhaust valves per cylinder is two or more, can be reduced.

TECHNICAL FIELD

A cam follower device according to the present invention is built in avalve train of an engine such as, for example, a three-valve engine,four-valve engine or five-valve engine in which the number of at leasteither of inlet valves and exhaust valves which are provided for onecylinder is two or more for converting rotation of a camshaft into areciprocating motion of the two inlet valves or two exhaust valves.

BACKGROUND ART

Excluding part of two-cycle engines, an inlet valve and an exhaust valvewhich are adapted to open and close in synchronism with rotation of acrankshaft are provided in reciprocating engines (reciprocating pistonengines). In reciprocating engines like these, the movement of thecamshafts which rotate in synchronism with rotation of the crankshaft(at one half crankshaft speed in the case of a four-cycle engine) istransmitted to the inlet valve and the exhaust valve by rocker arms, soas to cause the inlet valve and the exhaust valve to reciprocated in anaxial direction. In addition, it is general practice to build in atappet roller between the camshaft and the rocker arm with a view torealizing a reduction in friction within an interior of the engine so asto reduce the fuel consumption rate.

FIGS. 30 to 31 show a conventional cam follower device which isdescribed in Patent Document No. 1 as a first example of a conventionalconstruction of a cam follower device which includes the rocker arm andthe tappet roller described above. A rocker arm 3 constituting the camfollower device is provided at a portion which confronts a cam 2 fixedlyprovided on a camshaft 1 which rotates in synchronism with a crankshaftof an engine. A rocker arm shaft 5, which is a stationary shaft providedparallel to the camshaft 1, is inserted into a through hole 4 formed inan intermediate portion of the rocker arm 3. This configuration enablesa swinging displacement of the rocker arm 3 about the rocker arm shaft5.

In addition, a pair of support wall portions 6, 6 which are parallel toeach other is provided at one end portion (a right end portion in FIG.30) of the rocker arm 3 as shown in detail in FIG. 31. A support shaft 7is fixed to the one end portion so as to extend between the endportions. For this purpose, both end portions of the support shaft 7 arefixedly fitted, respectively, in a pair of support holes 8, 8 formed inboth the support wall portions 6, 6 in positions which are aligned witheach other.

In addition, a tappet roller 9 is supported rotatably on the peripheryof an intermediate portion of the support shaft 7 via a radial needlebearing 10. Then, an outer circumferential surface of this tappet roller9 is brought into an outer circumferential surface of the cam 2.

Additionally, a screw hole, not shown, is provided at the other endportion (a left end portion in FIG. 30) of the rocker arm 3, and anadjustment screw 11 is fixedly screwed into this screw hole. Then, adistal end portion (a pressing portion) of the adjustment screw 11 iscaused to strike a proximal end face of a valve element 12 which is aninlet valve or an exhaust valve.

When the engine is running, the rocker arm 3 is displaced in a swingingfashion about a center (a fulcrum) of the rocker arm shaft 5 inaccordance with rotation of the cam 2. Then, the rocker arm 3reciprocates the valve element 12 in an axial direction by pressingforce of the adjustment screw 11 and spring force of a return spring 13.As this time, the tappet roller 9 can reduce frictional force actingbetween the cam 2 and the rocker arm 3, and therefore, a reduction infuel consumption rate when the engine is running can be realized.

Next, FIGS. 32 to 34 show a cam follower device which is also describedin Patent Document No. 1 as a second example of a conventionalconstruction of a cam follower device including the rocker arm and thetappet roller. A rocker arm 3 a in the cam follower device of the secondexample of conventional construction is formed by applying to a sheetmetal, such as sheet steel, stamping process for removing unnecessaryportions and plastic process such as drawing process for obtaining adesired shape. Thus formed rocker arm 3 a includes a pair of supportwall portions 6 a, 6 a which are parallel to each other, a firstconnecting portion 14 which connects one end portions (right endportions in FIGS. 32 to 34) of these support wall portions 6 a, 6 a toeach other, and a second connecting portion 15 which connects the otherend portions (left end portions in FIGS. 32 to 34) thereof to eachother.

In addition, a tappet roller 9 is disposed between the support wallportions 6 a, 6 a and between the first and second connecting portions14, 15. This tappet roller 9 is supported rotatably around the peripheryof an intermediate portion of a support shaft 7 which is fixed directlyor via radial needle bearing to the support wall portions 6 a, 6 a so asto extend therebetween. In addition, both end portions of the supportshaft 7 are fittingly fixed, respectively, in a pair of support holes 8formed in both the support wall portions 6 a, 6 a in positions alignedwith each other for fixing the support shaft 7 at both the support wallportions 6 a, 6 a.

In an assembling state of the cam follower device to the valve train ofan engine, as shown in FIG. 34, a distal end face of a plunger 16constituting a lash adjuster is caused to strike a spherically recessedportion (a receiving portion) provided on one side (a lower side in FIG.34) of the first connecting portion 14 and a proximal end portion of thevalve element 12 which is the inlet valve or the exhaust valve is causedto strike one side (a lower side in FIG. 34) of the second connectingportion 15 (the pressing portion). In addition, an outer circumferentialsurface of a cam 2 fixedly provided at an intermediate portion of acamshaft 1 is brought into abutment with an outer circumferentialsurface of the tappet roller 9.

When the engine is running, in accordance with rotation of the cam 2,the rocker arm 3 a is displaced in a swinging fashion about an abutmentportion between the distal end face of the plunger 16 and thespherically recessed portion as a center (a fulcrum) between statesindicated by solid and chain lines in FIG. 34, so as to reciprocate thevalve element 12 in the axial direction by the pressing force of thesecond connecting portion 15 and the spring force of a return spring 13.As this time, the tappet roller 9 can reduce frictional force actingbetween the cam 2 and the rocker arm 3 a, and therefore, a reduction infuel consumption rate when the engine is running can be realized.

In addition, in either case of the conventional constructions that havebeen described above, as a method of fittingly fixing both the endportions of the support shaft 7 in the support holes 8, 8 which areformed in the pair of support wall portions 6, 6 (6 a, 6 a), it isconsidered to adopt a method of press fitting both the end portions ofthe support shaft 7 in both the support holes 8, 8, respectively. Ineither case of the conventional constructions, however, both the supportwall portions 6, 6 (6 a, 6 a) are formed integrally on the rocker arm 3(3 a), and a space between both the support wall portions 6, 6 (6 a, 6a) cannot be expanded. Therefore, when press fitting both the endportions of the support shaft 7 in both the support holes 8, 8,respectively, in a press fitting process, an intermediate portion of thesupport shaft 7 needs to be passed through an inside of either of thesupport holes 8 while being press fitted in either of the support holes8. As a result, there is a fear that an outer circumferential surface ofthe intermediate portion of the support shaft 7 is damaged. However,since the outer circumferential surface of the intermediate portion ofthis support shaft 7 has a function as an inner ring raceway of theradial needle bearing 10 (or an internal sliding surface of a slidebearing) which supports rotatably the tappet roller 9, the damagedescribed above is not preferred.

Thus, with a view to preventing the occurrence of such a drawback, afollowing fixing method has conventionally been adopted.

The conventional method is, after hardening only the outercircumferential surface of the intermediate portion of the support shaft7 by induction hardening,while inwardly fitting both the end portions of the support shaft 7 arefitted, respectively, in insides of both the support holes 8, 8 withoutlooseness and interference therebetween, outer circumferential edgeportions of both end faces of the support shaft 7 are compressed to beexpanded towards circumferential edge portions of openings of both thesupport holes 8, 8. However, the fixing method of this type needs anumber of steps and causes an increase in production costs.

Incidentally, in configuration of the valve train of the engine, whenonly conventional cam follower devices like one that has been describedabove are used as cam follower devices that are to be built in the valvetrain, the same numbers of cams 2 and tappet rollers 9 as valve elements12 are necessary. However, in association with the recent trend ofmulti-valve engines, the numbers of inlet valves and exhaust valves tobe provided per cylinder are gradually increased such as two or three.Therefore, in configuring the valve train of such a multi-valve engine,when only conventional cam follower devices like one that has beendescribed above are used, the number of components of the valve trainbecomes too many, and this easily calls for drawbacks of the valve trainbeing made enlarged in size, heavy in weight, highly frictional andhighly expensive in cost.

Patent Document No. 1: Japanese Patent Unexamined PublicationJP-A-2004-100499

DISCLOSURE OF THE INVENTION Problem that the Invention is to Solve

A cam follower device of the invention has been made in view of thesituations described above and an object thereof is to realize aconstruction which can reduce the numbers of cams and tappet rollerswhich are used when configuring a valve train of a multi-valve engine.

Means for Solving the Problem

The invention is attained by the following configurations.

(1) A cam follower device that is built in a valve train of an engine inwhich a number of at least one of inlet valves and exhaust valves whichare to be provided per cylinder is two or more, including:

a pair of rocker arms which are disposed parallel to each other with apredetermined interval provided therebetween and have a pair of supportholes which are concentric with each other at one end portions orintermediate portions thereof in positions which are aligned with eachother;

a support shaft which is fixed to both the rocker arms so as to beextended between the rocker arms by fitting both end portions in thesupport holes, respectively;

a tappet roller which is supported rotatably around a periphery of anintermediate portion of the support shaft, an outer circumferentialsurface of the tappet roller being capable of abutting with an outercircumferential surface of a cam which is fixed on a camshaft when thecam follower device is built in the valve train; and

a pair of pressing portions which are provided directly or via aseparate member at the other end portions of both the rocker arms, thepair of pressing portions being capable of striking individuallyproximal end faces of two inlet valves or two exhaust valves when thecam follower device is built in the valve train.

(2) The cam follower device as set forth in (1), wherein

the pair of rocker arms is formed separately.

(3) The cam follower device as set forth in (2), wherein

the pair of support holes are formed at the one end portions of the pairof rocker arms, and

a pair of through holes, into which a rocker arm shaft provided inparallel with the camshaft is capable of being inserted when the camfollower device is built in the valve train, are formed at theintermediate portions of the rocker arms in positions which are alignedwith each other, so as to enable a swinging displacement of both therocker arms.

(4) The cam follower device as set forth in (3), wherein

an interval between inner surfaces of both the rocker arms whichconfront each other are made relatively narrow at the one end portionsand relatively wide at the other end portions of both the rocker arms bymaking thickness of both the rocker arms relatively large at the one endportions and relatively small at the other end portions of both therocker arms.

(5) The cam follower device as set forth in (3), wherein

an interval between inner surfaces of both the rocker arms whichconfront each other are made relatively narrow at the one end portionsand relatively wide at the other end portions of both the rocker arms byproviding non-parallel plate portions which are not parallel to theintermediate portions of both the rocker arms at portions between theone end portions and the intermediate portions or between theintermediate portions and the other end portions of both the rockerarms.

(6) The cam follower device as set forth in (3), wherein

both end portions of a cylindrical sleeve are inwardly fitted and fixed,respectively, in the pair of through holes and

the rocker arm shaft is inserted into an inside of the sleeve.

(7) The cam follower device as set forth in (2), wherein

the pair of support holes are formed at the intermediate portions of thepair of rocker arms, and

the one end portions of both the rocker arms have a pair of receivingportions which are provided thereon directly or via separate members andwith which distal end faces of a pair of plungers is capable of beingbrought into abutment when the cam follower device is built in the valvetrain, so as to enable a swinging displacement of both the rocker armsabout abutment portions between the receiving portions and the distalend faces of the pair of plungers as fulcrums.

(8) The cam follower device as set forth in (7), wherein

an interval between inner surfaces of both the rocker arms whichconfront each other are made relatively narrow at the one end portionsand relatively wide at the other end portions of both the rocker arms bymaking thickness of both the rocker arms relatively large at the one endportions and relatively small at the other end portions of both therocker arms.

(9) The cam follower device as set forth in (7), wherein

an interval between inner surfaces of both the rocker arms whichconfront each other are made relatively narrow at the one end portionsand relatively wide at the other end portions of both the rocker arms byproviding non-parallel plate portions which are not parallel to theintermediate portions of both the rocker arms at portions between theone end portions and the intermediate portions or between theintermediate portions and the other end portions of both the rockerarms.

(10) The cam follower device as set forth in (1), wherein

an axial displacement amount allowed to the tappet roller is controlledto a desired magnitude by disposing spacers which are fitted on thesupport shaft, respectively, between inner surfaces of both the rockerarms and both axial end faces of the tappet roller.

(11) The cam follower device as set forth in (1), wherein

thickness of portions of both the rocker arms which need to have ahigher strength than that of peripheral areas thereof are larger thanthickness of the peripheral areas.

(12) The cam follower device as set forth in (2), wherein

the pair of rocker arms is each formed by applying stamping process to asingle sheet metal.

(13) The cam follower device as set forth in (1), wherein

the pair of rocker arms is connected together by a connecting portionprovided in at least one location so as to prohibit a relativedisplacement.

(14) The cam follower device as set forth in (13), wherein

the pair of support holes are formed at the one end portions of the pairof rocker arms, and

a pair of through holes into which a rocker arm shaft provided inparallel with the camshaft is capable of being inserted when the camfollower device is built in the valve train, are formed at theintermediate portions of the rocker arms in positions which are alignedwith each other, so as to enable a swinging displacement of both therocker arms.

(15) The cam follower device as set forth in (13), wherein

the pair of rocker arms which are connected together by the connectingportion provided in at least the one location so as to prohibit arelative displacement are made by applying stamping process and bendingprocess to a single sheet metal.

ADVANTAGE OF THE INVENTION

When the valve train of the engine in which the number of at least oneof the inlet valves and the exhaust valves which are to be provided percylinder is two or more is configured using the cam follower device ofthe invention, the two inlet valves or the two exhaust valves can beopened and closed simultaneously only by providing the single cam andthe single tappet roller. Thus, as the cam follower device that is to bebuilt in the valve train, the cam follower device can realize areduction in the number of components of the valve train, when comparedwith the above described conventional cam follower device. Consequently,the valve train can be made smaller in size (space saving) and lighterin weight and can realize reductions in friction and production costs.

In addition, in the cam follower device of the invention, as the methodof fittingly fixing both the end portions of the support shaft in thesupport holes, the method of press fitting both the end portions of thesupport shaft in both the support holes can be adopted.

In addition, when this method is adopted, the outer circumferentialsurface of the support shaft {the inner ring raceway of the radialneedle bearing (or the inner sliding surface of the slide bearing) forsupporting the tappet roller rotatably} can be prevented from beingdamaged. This is because when the invention which has the pair rockerarms which are disposed parallel to each other with the predeterminedinterval (at the same pitch as the pitch of the two valve elements whichare to be opened and closed simultaneously) and which have the pair ofsupport holes, both the end portions of the support shaft can be pressfitted, respectively, in the insides of both the support holes throughthe openings of the support holes which lie on sides thereof opposing toeach other.

In other words, in the invention which is different from the abovedescribed respective conventional constructions, in the step of pressfitting both the end portions of the support shaft, respectively, in thepair of support holes, it is not necessary to cause the support shaft topass through the inside of either of the support holes while theintermediate portion of the support shaft is press fitted (fittedthrough interference fit) in either of the support holes.

In addition, when assembling the cam follower device of the invention,when the above described method of press fitting (fitting throughinterference fit) both the end portions of the support shaft in the pairof support holes is adopted, since the necessity is obviated ofcompressing to expand both ends of the support shaft, it is notnecessary to keep both the ends of the support shaft in a raw state (astate in which no hardening treatment has been applied). Consequently, aso-called immersion quenching in which the whole of the support shaft isheated and is then immersing the heated support shaft in hardening oilcan be applied as the hardening of the support shaft. Since thehardening treatment using immersion quenching is lower in cost than thehardening treatment using induction hardening, the production costs canbe lowered due to the immersion quenching.

The pair of rocker arms of the invention which can prevent the damage tothe outer circumferential surface of the intermediate portion of thesupport shaft may be parts which are separate from each other.

Further, the pair of rocker arms of the invention may be constructedsuch that although the pair of rocker arms are connected together by aconnecting portion in at least one location so that the rocker arms aredisabled from a relative displacement, a distance between the portionswhere the support holes are formed and the connecting portion is maderelatively large so that the interval between the rocker arms can beexpanded.

In addition, when both the rocker arms are connected together by aconnecting portion in at least one location so that the rocker arms aredisabled from a relative displacement, the phase aligning operationbecomes unnecessary which has conventionally been performed when the camfollower device is assembled onto the engine.

Additionally, when the cam follower device set forth under (3) iscarried out, in the event that the configurations set forth under (4),(5) are adopted, even if the interval between the proximal end faces ofthe two inlet valves or two exhaust valves which are to be pressed bythe pair of pressing portions is made remarkably large compared with theaxial dimension of the tappet roller, the pair of pressing portionswhich can press both the proximal end faces accurately can be providedand the intervals between both the axial end faces of the tappet rollerand the inner surfaces of the pair of rocker arms can be made smallsufficiently (the axial displacement permitted to the tappet roller canbe controlled to the desired magnitude). In other words, it becomesunnecessary to increase the axial dimension of the tappet roller so asto match the interval between both the proximal end faces.

In addition, when the cam follower device set forth under (3) to (5) iscarried out, if adapting the configuration set forth under (6), sinceboth the end portions are fittingly fixed, respectively, in both thethrough holes provided in the intermediate portions of the pair ofrocker arms, displacement of the positional relationship between boththe rocker arms can effectively be prevented from a proper positionalrelationship.

Consequently, the occurrence of a drawback associated with such adisplacement can be prevented effectively. (As the drawback associatedwith the displacement, followings can be exemplified. A drawbackoccurring when the cam follower device is assembled such as thedifficulty in insertion of the rocker arm shaft into both the throughholes, a drawback of displacement in phases of the two inlet valves orexhaust valves which are to be pressed by the cam follower devicedeviate from each other when using and a drawback of occurrence ofpartial contact in which the outer circumferential surface of the tappetroller and the outer circumferential surface of the cam do not contactin parallel due to the inclination of the center axis of the tappetroller.)

Additionally, not inner circumferential surfaces of both the throughholes whose axial dimension is small but an inner circumferentialsurface of the sleeve whose axial dimension is sufficiently large isbrought into slide contact with the outer circumferential surface of therocker arm shaft. Thus, a sliding area relative to the outercircumferential surface of the rocker arm shaft can be securedsufficiently, whereby wear amount of the outer circumferential surfaceof the rocker arm shaft can be made sufficiently small. Accordingly,duration life of the rocker arm shaft can be increased. In addition,since the inner circumferential surfaces of both the through holes donot have to be brought into slide contact with the outer circumferentialsurface of the rocker arm shaft, the thickness of both the rocker armscan be made thinner by such an amount.

In addition, when the cam follower device set forth under (7) is carriedout and the configurations set forth under (8), (9) are adopted, even ifthe interval between the proximal end faces of the two inlet or exhaustvalves to be pressed by the pair of pressing portions and the intervalbetween the distal end faces of the pair of plungers to be made tostrike the pair of receiving portions become remarkably large comparedwith the axial dimension of the tappet roller, the pair of pressingportions which can press both the proximal end faces accurately and thepair of receiving portions having both the distal end faces made tostrike accurately can be provided and also the intervals between boththe axial end faces of the tappet roller and the inner surfaces of thepair of rocker arms can be made small sufficiently (the axialdisplacement permitted to the tappet roller can be controlled to thedesired magnitude). In other words, it becomes unnecessary to increasethe axial dimension of the tappet roller so as to match the intervalbetween both the proximal end faces and the interval between both thedistal end faces.

Additionally, when the cam follower device set forth under (1) iscarried out and the configuration set forth under (10) is adopted, evenif the interval between the inner surfaces of the pair of rocker armsbecomes remarkably large compared with the axial dimension of the tappetroller, the axial displacement that is permitted to the tappet rollercan be controlled to the desired magnitude. Consequently, if theconfiguration described under (10) is adopted, a common tappet roller(and a radial rolling bearing such as the radial needle bearing providedradially inside the tappet roller) can be used for pairs of rocker armshaving various shapes. In addition, the shape of a pair of rocker armscan be determined so as to match the layout of an engine.

Furthermore, when the cam follower device set under (1) is carried outand the configuration set forth under (11) is adopted, compared with aconstruction in which the thickness dimension of a pair of rocker armsis increased overall, the strength at part of both the rocker arms canbe increased accurately without calling for a wasteful and meaninglessincrease in weight.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side view showing a state in which a first embodiment of theinvention is built in a valve train of an engine.

FIG. 2 is a view as viewed from the top of FIG. 1.

FIG. 3 is a sectional view taken along the line III-III in FIG. 1.

FIG. 4 is an enlarged view of a portion denoted as IV in FIG. 1.

FIG. 5 is a similar diagram to FIG. 4, which shows a first example of arocker arm of a different construction.

FIG. 6( a) is a view as viewed in the same direction as FIG. 2, whichshows a second example of a rocker arm of a different construction inapartially sectioned state, and FIG. 6( b) is an end view of the secondexample.

FIG. 7( a) is a view as viewed in the same direction as FIG. 2, whichshows a third example of a rocker arm of a different construction in apartially sectioned state, and FIG. 7( b) is an end view of the secondexample.

FIG. 8 is a view as viewed in the same direction as FIG. 2, which showsa fourth example of a rocker arm of a different construction in apartially sectioned state.

FIG. 9 is a view as viewed in the same direction as FIG. 2, which showsa fifth example of a rocker arm of a different construction in apartially sectioned state.

FIG. 10 is a diagram similar to FIG. 2, which shows a second embodimentof the invention.

FIG. 11 is a diagram of a left end portion of an upper rocker arm inFIG. 10 as viewed from an internal surface side of the left end portion.

FIG. 12 is a view as viewed in the same direction as FIG. 2, which showsa third embodiment of the invention.

FIG. 13 is a diagram similar to FIG. 2, which shows a fourth embodimentof the invention in a partially sectioned state.

FIG. 14 is a perspective view showing a construction which is notpreferred when compared with the construction of the fourth embodiment.

FIG. 15 is a diagram similar to FIG. 2, which shows a fifth embodimentof the invention in a partially sectioned state.

FIG. 16 is a diagram similar to FIG. 2, which shows a sixth embodimentof the invention.

FIG. 17 is a diagram similar to FIG. 1, which shows a seventh embodimentof the invention.

FIG. 18 is a diagram as viewed from the top of FIG. 17, which shows thesame embodiment in a partially sectioned state.

FIG. 19 is a diagram corresponding to a central portion of FIG. 18,which shows an eighth embodiment of the invention.

FIG. 20 is a side view showing a ninth embodiment of the invention insuch a state that it is built in the valve train of the engine.

FIG. 21 is a view as viewed from the top of FIG. 20 with part thereofomitted.

FIG. 22 A sectional view taken along the line XXII-XXII in FIG. 20.

FIG. 23 is a diagram similar to FIG. 2, which shows a tenth embodimentof the invention.

FIG. 24A is a diagram similar to FIG. 2, which shows a modified exampleto the tenth embodiment of the invention, and FIG. 24B is a diagramsimilar to FIG. 2, which shows another modified example to the tenthembodiment of the invention.

FIG. 25 is a side view showing a state in which an eleventh embodimentof the invention is built in the valve train of the engine.

FIG. 26 is a view as viewed from the top of FIG. 25.

FIG. 27A is a diagram illustrating a first step in which stampingprocess is applied to a sheet metal for forming rocker arms, and FIG.27B is a diagram illustrating a second step in which bending process isapplied to the stamped sheet metal for forming rocker arms.

FIG. 28 is a view resulting when rocker arms are viewed from thereabovewhich are constructed such that cylindrical portions are formed atthrough holes.

FIG. 29 is a perspective view of rocker arms which are constructed suchthat cylindrical portions are formed at through holes.

FIG. 30 is a partial side view of a valve train of an engine in which afirst example of a conventional cam follower device is built.

FIG. 31 is an enlarged sectional view taken along the line XXXI-XXXI inFIG. 30.

FIG. 32 is a perspective view showing a second example of a conventionalcam follower device.

FIG. 33 is a sectional view taken along the line XXXIII-XXXIII in FIG.32.

FIG. 34 is a partially sectional view of a valve train of an engine inwhich a second example of a conventional cam follower device is built.

DESCRIPTION OF REFERENCE NUMERALS

1 camshaft; 2 cam; 3, 3 a rocker arm; 4, 4 a through hole; 5 rocker armshaft; 6, 6 a support wall portion; 7, 7 a support shaft; 8, 8 a supporthole; 9 tappet roller; 10 radial needle bearing; 11 adjustment screw; 12valve element; 13 return spring; 14 first connecting portion; 15 secondconnecting portion; 16 plunger; 17, 17 a-17 r rocker arm; 18 projectingportion; 19 holding piece; 20 recessed portion; 21 pressing plateportion; 22 flat plate portion; 23 cylindrical portion; 24 through hole(or screw hole); 25 cylindrical portion; 26 cylindrical portion; 27cylindrical member; 28 sleeve; 29 sleeve; 30 spherically recessedportion; 31, 31 a thick portion; 32 ring spacer; 33 cylindrical spacer;34 thick portion; 35, 35 a, 35 b inclined plate portion; 36 radialneedle bearing; 37 ring plate; 38 connecting portion; 39 cylindricalportion.

BEST MODE FOR CARRYING OUT THE INVENTION First Embodiment

FIGS. 1 to 4 show a first embodiment of the invention. A cam followerdevice of this embodiment is built, for use, in a valve train of anengine (of an OHC or DOHC type) such as, for example, a three-valveengine, a four-valve engine or a fifth-valve engine in which the numberof at least one of inlet valves and exhaust valves provided per cylinderis made to be two or more. The cam follower device of the embodimentthat is so designed includes a pair of plate-shaped rocker arms 17, 17which are identical in shape and size to each other, a support shaft 7 aand a tappet roller 9.

In these constituent parts, the pair of plate-shaped rocker arms 17, 17is formed separately into a shape like a boomerang by applying stampingprocess to a sheet metal such as a sheet steel. The two so formed rockerarms 17, 17 are disposed parallel to each other with a predeterminedinterval defined therebetween. In addition, the support shaft 7 a isfixed to one end portions (right end portions in FIGS. 1 to 2) of boththe rocker arms 17, 17 so as to be extended therebetween. For thispurpose, a pair of support holes 8 a, 8 a is formed concentric with eachother in positions which are aligned with each other at the one endportions of both the rocker arms 17, 17. Then, after a hardeningtreatment by immersion quenching is applied to a whole surface of thesupport shaft 7 a, both end portions of the support shaft 7 a are pressfitted, respectively, in insides of both the support holes 8 a, 8 athrough openings of the support holes 8 a, 8 a which lie on sidesthereof opposing to each other.

In addition, in this embodiment, in a state of the support shaft 7 abeing press fitted, by bringing male serrations (not shown) formed onouter circumferential surfaces of both the end portions of the supportshaft 7 a and female serrations (not shown) formed on innercircumferential surfaces of both the support holes 8 a, 8 a intoengagement with each other (or causing ridge portions of the maleserrations to bite into the inner circumferential surfaces of thesupport holes), relative rotation at the press fitted portions isprevented effectively. In other words, both the rocker arms 17, 17prevent the relative swing between the rocker arms about the supportshaft 7 a effectively.

In addition, in press fitting the end portions of the support shaft 7 a,respectively, in the pair of support holes 8 a, 8 a, and serrations maybe provided on at least either of the outer circumferential surfaces ofthe end portions of the support shaft 7 a and the inner circumferentialsurfaces of the support holes 8 a, 8 a.

In addition, the tappet roller 9 is supported rotatably on an outercircumferential surface of an intermediate portion of the support shaft7 a via a radial needle bearing 10. Additionally, a pair of throughholes 4, 4 which is concentric with each other is formed at intermediateportions of both the rocker arms 17, 17 in positions aligned with eachother. In addition, a pair of projecting portions 18, 18 (pressingportions) is provided on lower sides of the other end portions (left endportions in FIGS. 1 to 2) of both the rocker arms 17, 17. Distal endfaces of both the projecting portions 18, 18 are each made into apartially cylindrical surface. In addition, it is adaptable to supportthe tappet roller 9 rotatably on the circumference of the intermediateportion of the support shaft 7 a via the radial rolling bearing such asthe radial needle bearing 10, it is also adaptable to support the tappetroller 9 rotatably on the support shaft 7 a directly or via a slidebearing.

By using the radial rolling bearing as in this embodiment, swingresistance of the pair of rocker arms 17, 17 about the rocker arm shaft5 can be reduced and also the fuel consumption rate at the running ofthe engine can be reduced.

As shown in FIGS. 1 to 2, in a state of assembling the cam followerdevice to the valve train of the engine, the rocker arm shaft 5 as astationary shaft is inserted into the respective through holes 4, 4without looseness and no interference therebetween so as to enable theswinging displacement of both the rocker arms 17, 17 about the rockerarm shaft 5. In conjunction with this, an outer circumference of thetappet roller 9 is brought into abutment with an outer circumferentialsurface of a cam 2 which is fixedly provided on a camshaft 1, and thedistal end faces of both the projecting portions 18, 18 are caused tostrike individually proximal end faces of two valve elements 12, 12 (twoinlet valves or two exhaust valves which are provided for the samecylinder). When the engine is running, both the rocker arms 17, 17 areswung about the rocker arm shaft 5 as the cam 2 rotates, so as toreciprocate the two valve elements 12, 12 in an axial direction bypressing force exerted by both the projecting portions 18, 18 and springforce by the return spring 13 (which is omitted in FIGS. 1 to 4. Referto FIGS. 30, 34).

As has been described, when the cam follower device of the embodiment isused, only by providing the single cam 2 and the single tappet roller 9,the two valve elements 12, 12 can be reciprocated simultaneously. Thus,when compared with the case where only the aforesaid conventional camfollower device is used as the cam follower device to be built in thevalve train (the independent cam follower device is built in for eachvalve element), the number of parts in the valve train can be reduced.Consequently, the resulting valve train can be made smaller in size(space saving) and lighter in weight and can realize reductions infriction and production costs. In addition, according to thisembodiment, both the end portions of the support shaft 7 a can be pressfitted in the pair o support holes 8 a, 8 a without damaging the outercircumferential surface of the intermediate portion of the support shaft7 a. Thus, as a hardening treatment applied to the surface of thesupport shaft 7 a, an immersion quenching which is more inexpensive thaninduction hardening can be adopted. Consequently, the production costscan be suppressed.

In addition, as has been described above, it is only required for boththe rocker arms 17, 17 to be formed in the same shape and size, then,the positional relationship between both the rocker arms 17, 17 can bemade proper, whereby the occurrence of a difference in contact statewith their mating parts such as the valves can be prevented effectively.

Note that when carrying out the cam follower device of the embodiment,rocker arms 17 a to 17 e which are shown in FIGS. 5 to 9 can also beused as the pair of rocker arms. These rocker arms 17 a to 17 e differfrom the rocker arm 17 that has been described heretofore in shape of atleast the other end portions (left end portions in FIGS. 5 to 9)thereof.

In these rocker arms, firstly, in the rocker arm 17 a shown in FIG. 5, apair of holding pieces 19, 19 is projectingly provided on both front andrear sides (left- and right-hand sides in FIG. 5) of a projectingportion 18 provided on a lower surface of the other end portion thereof.

In the rocker arm 17 b shown in FIG. 6, a pressing plate portion 21having U-shaped cross section provided with a recessed portion 20 on alower surface thereof is provided at the other end thereof, and a bottomsurface of the recessed portion 20 is made into a pressing portioncaused to strike a proximal end face of the valve element.

In the rocker arm 17 c shown in FIG. 7, a flat plate portion 22 which isperpendicular to one end portion (a right end portion in FIG. 7) to anintermediate portion is provided at the other end portion, hole openingwork is applied to a central portion of this flat plate portion 22 andthen, burring process is applied to the portion to which the holeopening work is applied so as to form a cylindrical portion 23. Then, aninside of this cylindrical portion 23 is made into a through hole (or ascrew hole) 24. When using this rocker arm 17 c, a distal end portion ofan adjustment pin (or an adjustment screw), not shown, which isfittingly fixed in the through hole (or the screw hole) 24 is made intoa pressing portion caused to strike the proximal end face of the valveelement.

In the rocker arm 17 d shown in FIG. 8, a cylindrical portion 25 isformed integrally at the other end portion by bending process. An insideof the cylindrical portion 25 is made into a through hole (or a screwhole) 24 in which the aforesaid adjustment pin (or the adjustmentscrew), not shown, is fittingly fixed (or screw fixed). Additionally, inorder to secure an insertion length of the rocker arm shaft 5 (refer toFIG. 2) relative to a through hole 4 provided in an intermediate portionof the rocker arm 17 d, burring process is applied to a peripheralportion of the through hole 4 so as to form a cylindrical portion 26.

In addition, in the rocker arm 17 e shown in FIG. 9, a cylindricalmember 27 is fixedly joined to the other end portion through welding,electric welding or the like. Then, an inside of the cylindrical member27 is made into a through hole (or a screw hole) 24 in which theaforesaid adjustment pin (or the adjustment screw), not shown, isfittingly fixed (or screw fixed). Additionally, in order to secure aninsertion length of the rocker arm shaft 5 (refer to FIG. 2) relative toa through hole 4 provided in an intermediate portion of the rocker arm17 e, a sleeve 28 is fittingly fixed in an inside of the through hole 4,so that the rocker arm shaft 5 is made to be inserted into an inside ofthe sleeve 28.

Second Embodiment

Next, FIGS. 10 to 11 show a second embodiment of the invention. In thisembodiment, in order to increase the strength at the other end portions(left end portions in FIG. 10) of a pair of rocker arms 17 h, 17 h whereprojecting portions 18, 18 are provided, both the end portions are madeinto thick portions 31, 31. In order to form both the thick portions 31,31, in this embodiment, internal surfaces of the other end portions ofboth the rocker arms 17 h, 17 h are caused to swell. Thus, a thicknessdimension T of the other end portions (the thick portions 31, 31) ofboth the rocker arms 17 h, 17 h is made larger than a thicknessdimension t of one end portions and intermediate portions thereof (T>t).In this embodiment which is configured in the way described above,compared to a construction in which a thickness dimension of both therocker arms 17 h, 17 h is increased along the full length thereof, thestrength at both the end portions can be increased accurately withoutcalling for a wasteful and meaningless increase in weight. The otherconfiguration and function of this embodiment are similar to those ofthe first embodiment described before.

Third Embodiment

Next, FIG. 12 shows a third embodiment of the invention. In thisembodiment, too, in order to increase the strength at the other endportions (left end portions in FIG. 12) of a pair of rocker arms 17 i,17 i where projecting portions 18, 18 are provided, both the other endportions are made into thick portions 31 a, 31 a. However, in the caseof this embodiment, in order to form both the thick portions 31 a, 31 a,both side surfaces of the other end portions of both the rocker arms 17i, 17 i are caused to swell. The other configuration and function ofthis embodiment are similar to those of the second embodiment describedabove.

Fourth Embodiment

Next, FIG. 13 shows a fourth embodiment of the invention. In thisembodiment, compared to the above described respective embodiments, aninterval between a pair of valve elements 12, 12 which are to be pressedbecomes remarkably large. Due to this, in this embodiment, an intervalbetween a pair of rocker arms 17 i, 17 i is made remarkably largecompared to the aforementioned respective embodiments so as to match theinterval between both the valve elements 12, 12. In contrast to this, inthis embodiment, as a tappet roller 9 disposed between one end portions(right end portions in FIG. 13) of both the rocker arms 17 i, 17 i, atappet roller 9 is used which has the same axial dimension as those ofthe respective embodiments. Thus, in this embodiment, widths of gapswhich reside between internal surfaces of the one end portions of boththe rocker arms 17 i, 17 i and both axial end faces of the tappet roller9 are both made far larger than a permissible axial displacement of thetappet roller 9.

Here, as shown in FIG. 14, if a construction is adopted, in which nomember is disposed in portions defined between the internal surfaces ofthe one end portions (right end portions in FIG. 14) of both the rockerarms 17 i, 17 i and both the axial end faces of the tappet roller 9, thetappet roller 9 would be allowed to be displaced in axial directions bya distance equal to the widths of the gaps residing in the portions. Asa result, when the engine is running, the tappet roller 9 is displacedlargely in the axial direction, whereby there emerges a possibility thata drawback is caused, such as a radial needle bearing 10 disposedradially inwards of the tappet roller 9 being dislocated outwards of thetappet roller 9 or the tappet roller 9 being disengaged from the cam 2,and hence, the construction is not preferred. In order to avoid such asituation, although it is considered that the axial dimension of thetappet roller 9 is increased so as to match the interval between theinternal surfaces of both the rocker arms 17 i, 17 i. However, since adrawback of increasing of the weight of the tappet roller 9 will becaused and it makes difficult for the engine to revolve at higher speedsor the fuel consumption rate at the time of running of the engine isincreased, thus, such a construction is not preferred.

Then, with a view to preventing the occurrence of the drawbacksdescribed above, in this embodiment shown in FIG. 13, a ring spacer 32and a cylindrical spacer 33 which are both fitted on a support shaft 7 aare disposed in each of the gaps between the internal surfaces of theone end portions of both the rocker arms 17 i, 17 i and both the axialend faces of the tappet roller 9 in this order from the tappet roller 9side while eliminating large looseness in the axial direction. Then, theaxial displacement permitted to the tappet roller 9 (and the radialneedle bearing 10) is controlled to a desired magnitude (a minuteamount) by the respective ring spacers 32, 32 and the respectivecylindrical spacers 33, 33. The other configuration and function of thisembodiment are similar to those of the third embodiment that has beendescribed above.

Fifth Embodiment

Next, FIG. 15 shows a fifth embodiment of the invention. In thisembodiment, in place of omitting the pair of cylindrical spacers 33, 33(refer to FIG. 13), internal surfaces of one end portions (right endportions in FIG. 15) of a pair of rocker arms 17 k, 17 k are caused toswell into thick portions 34, 34. By this configuration, an intervalbetween the internal surfaces of the one end portions of both the rockerarms 17, 17 is narrowed, so that an axial displacement permitted to atappet roller 9 is controlled to a desired magnitude (a minute amount).The other configuration and function of this embodiment are similar tothose of the fourth embodiment that has been described above except forthe fact that no thick portion is provided at the other end portions(left end portions in FIG. 15) of both the rocker arms 17 k, 17 k.

Sixth Embodiment

Next, FIG. 16 shows a sixth embodiment of the invention. In thisembodiment, in place of omitting the pairs of ring spacers 32, 32 andcylindrical spacers 33, 33 (refer to FIG. 13), inclined plate portions35, 35 (non-parallel plate portions) are formed between one end portions(right end portions in FIG. 16) to intermediate portions and the otherend portions (left end portions in FIG. 16) of a pair of rocker arms 17m, 17 m so as to be inclined in directions in which the inclined plateportions 35, 35 approach each other as they extend towards the one endportions. By this configuration, an interval between internal surfacesof the one end portions of both the rocker arms 17 m, 17 m is narrowed,so as to control an axial displacement permitted to a tappet roller 9 toa desired magnitude (a minute amount). The other configuration andfunction are similar to those of the aforesaid fourth embodiment shownin FIG. 13 except for the fact that no thick portion is provided at theother end portions (left end portions in FIG. 15) of both the rockerarms 17 m, 17 m.

Seventh Embodiment

Next, FIGS. 17 to 18 show a seventh embodiment of the invention. In thisembodiment, by press fitting both end portions of a cylindrical sleeve29, respectively, in insides of through holes 4 a, 4 a formed,respectively, at intermediate portions of a pair of rocker arms 17 f, 17f, the sleeve 29 is fixed to both the rocker arms 17 h, 17 f so as to beextended therebetween.

In addition, by bringing male serrations (not shown) formed on outercircumferential surfaces of both end portions of the sleeve 29 intoengagement with female serrations (not shown) formed on innercircumferential surfaces of both the through holes 4 a, 4 a, relativerotation at the press fitted portions is prevented effectively. Then, arocker arm shaft 5 is inserted into an inside of thus formed sleeve 29.

In the cam follower device of this embodiment, since the pair of rockerarms 17 f, 17 f are coupled together by the above sleep 29, a drawbackof displacement of the both the rocker arms 17 f, 17 f relative to eachother can be prevented more effectively. Namely, the displacement of apositional relationship between both the rocker arms 17 f, 17 f from aproper positional relationship can be prevented effectively.Consequently, drawbacks associated with such a displacement can beprevented effectively. (As the drawback associated with thedisplacement, followings can be exemplified. A drawback occurring whenthe cam follower device is assembled such as the difficulty in insertionof the rocker arm shaft 5 into both the through holes 4 a, 4 a, adrawback of displacement in phases of the two valves 12, 12 which are tobe pressed when using and a drawback of occurrence of partial contact inwhich the outer circumferential surface of the tappet roller 9 and theouter circumferential surface of the cam 2 do not contact in paralleldue to the inclination of the center axis of the tappet roller 9.)

Additionally, the inner circumferential surfaces of both the throughholes 4 a, 4 a whose axial dimension is small but an innercircumferential surface of the sleeve 29 whose axial dimension issufficiently large is brought into slide contact with an outercircumferential surface of the rocker arm shaft 5. Thus, a sliding arearelative to the outer circumferential surface of the rocker arm shaft 5can be secured sufficiently, whereby wear amount at the outercircumferential surface of the rocker arm shaft 5 can be madesufficiently small. As a result, the duration of life of the rocker armshaft 5 can be increased.

In addition, since it is not necessary to bring the innercircumferential surfaces of both the through holes 4 a, 4 a into slidecontact with the outer circumferential surface of the rocker arm shaft5, the thickness of both the rocker arms 17 f, 17 f can be made thinner.

Further, lubricant is supplied between the inner circumferential surfaceof the sleeve 29 and the outer circumferential rocker arm shaft 5 fromopenings at the end portions of the sleeve 29 during the running of theengine, whereby frictional force acting between both the circumferentialsurfaces is reduced sufficiently. Further, when carrying out thisembodiment, if forming oil communication holes on at least one portionof an intermediate portion of the sleeve 29, which penetrate theportions in radial direction, the lubricant can be supplied to both thecircumferential surface by this oil communication hole. Additionally, inthis embodiment, too, the aforesaid shapes of the other end portions ofthe rocker arms 17 a to 17 e, 17 h, 17 i which are shown in FIGS. 5 to12 can be adopted as the shape of the other end portions of the pair ofrocker arms. The other configuration and function are similar to thoseof the aforesaid first embodiment which is shown in FIGS. 1 to 4.

Eighth Embodiment

Next, FIG. 19 shows an eighth embodiment of the invention. In thisembodiment, a radial needle bearing 36 is provided between an innercircumferential surface of a cylindrical sleeve 29 and an outercircumferential surface of a rocker arm shaft 5. In conjunction withthis, a pair of circular ring plates 37, 37 are fixedly joined toexternal surfaces of a pair of rocker arms 17 f, 17 f at peripheralportions of through holes 4 a, 4 a so that inner circumferential edgesthereof are made to closely confront the outer circumferential surfaceof the rocker arm shaft 5. Thus, the radial needle bearing 36 isprevented from being dislocated to an outside of the sleeve 29 throughopenings at both ends thereof by inner circumferential edge portions ofboth the circular ring plates 37, 37. According to the cam followerdevice of this embodiment, since the swing resistance of the pair ofrocker arms 17 f, 17 f about the rocker arm shaft 5 can be reduced bythe radial needle bearing 36, the fuel consumption rate at the runningof the engine can be reduced. The other configuration and function ofthis embodiment are similar to those of the aforesaid seventhembodiment.

Ninth Embodiment

Next, FIGS. 20 to 22 show a ninth embodiment of the invention. In thisembodiment which is different from the heretofore described first toeighth embodiments, a tappet roller 9 is supported rotatably around acircumference of a support shaft 7 a via a radial needle bearing 10 andis disposed in an interval portion defined between intermediate portionsof a pair of plate-shaped rocker arms 17 g, 17 g. Therefore, in thisembodiment, a pair of support holes 8 a, 8 a in which both end portionsof the support shaft 7 a are press fitted (brought into serratedengagement with) are formed concentric with each other at theintermediate portions of the pair of plate-shaped rocker arms 17 g, 17 gin positions aligned with each other. In addition, spherically recessedportions 30, 30 (receiving portions) are provided on lower surfaces ofone end portions (right end portions in FIGS. 20 to 21) of both therocker arms 17 g, 17 g. In contrast to this, projecting portions 18, 18which are similar to those in the aforesaid first to second embodimentsare provided on lower surfaces of the other end portions (left endportions in FIGS. 20 to 21) of both the rocker arms 17 g, 17 g.

In an assembling state of the cam follower device of this embodiment tothe valve train of the engine, as shown in FIGS. 20 to 21, distal endfaces of a pair of plungers 16, 16 which make up lash adjusters arecaused to strike the spherically recessed portions 30, 30, respectively,and proximal end faces of two valve elements 12, 12 (two inlet valves ortwo exhaust valves which are provided for the same cylinder) are causedto strike distal end faces of both the projecting portions 18, 18,respectively. In association with this, an outer circumferential surfaceof a cam 2 fixed at an intermediate portion of a camshaft 1 is broughtinto abutment with an outer circumferential surface of the tappet roller9. When the engine is running, in accordance with the rotation of thecam 2, both the rocker arms 17 g, 17 g are displaced in a swingingfashion about the abutment portion between the distal end faces of boththe plungers 16, 16 and both the spherically recessed portions 30, 30 ascenters (fulcrums) of their swing, so as to reciprocate the two valveelements 12, 12 in an axial direction by pressing force exerted by boththe projecting portions 18, 18 and spring force by a return spring 13(which is omitted in FIGS. 20 to 22. Refer to FIGS. 30, 34.).

As has been described above, also when making up a valve train by theuse of the cam follower device of this embodiment, only by providing thesingle cam 2 and the single tappet roller 9, the two valve elements 12,12 can be made to reciprocate simultaneously. Thus, compared with thecase where only the conventional cam follower devices are built in thevalve train, the use of the cam follower device of this embodiment as acam follower device to be built in the valve train can reduce the numberof components involved in the valve train. Consequently, the resultingvalve train can be made smaller in size (space saving) and lighter inweight and can realize reductions in friction and production costs.

In addition, in this embodiment, too, similar to the cases of theaforesaid first to eighth embodiments, both the end portions of thesupport shaft 7 a can press fitted in the support holes 8 a, 8 a withoutdamaging an outer circumferential surface of an intermediate portion ofthe support shaft 7 a. Therefore, as a hardening treatment applied tothe surface of the support shaft 7 a, an immersion quenching which ismore inexpensive than induction hardening can be adopted. Consequently,the production costs can be suppressed.

In addition, in this embodiment, too, the aforesaid shapes of the otherend portions of the rocker arms 17 a to 17 e, 17 h, and 17 i shown inFIGS. 5 to 12 can be adopted as the shape of the other end portions ofthe pair of rocker arms. In addition, as to the receiving portions,various constructions can be adopted including a construction in whichthey are formed directly or via separate members at the one end portionsof both the rocker arms. For example, a construction can also be adoptedin which screw holes are provided at the one end portions of both therocker arms and adjustment screws whose distal end portions are madeinto receiving portions are fixedly screwed into the screw holes,respectively.

Tenth Embodiment

Next, FIG. 23 shows a tenth embodiment of the invention. In thisembodiment, an interval between distal end faces of a pair of plungers16, 16 which constitute fulcrums and an interval between proximal endfaces of a pair of valve elements 12, 12 which are to be pressed becomefar larger than those of the ninth embodiment. In contrast to this, inthe case of this embodiment, as a tappet roller 9 which is disposedbetween intermediate portions of a pair of rocker arms 17 n, 17 n, atappet roller 9 is used which has the same axial dimension as that ofthe tappet roller of the ninth embodiment. Therefore, in thisembodiment, inclined plate portions 35 a, 35 b (non-parallel plateportions) are formed, respectively, between one end portions (right endportions in FIG. 23) and intermediate portions of both the rocker arms17 n, 17 n and between the other end portions (left end portions in FIG.23) and the intermediate portions of both the rocker arms 17 n, 17 n soas to be inclined in directions in which the inclined plate portionscome nearer to each other as they extend towards the intermediateportions.

By this configuration, an interval between the one end portions of boththe rocker arms 17 n, 17 n is expanded so as to match the intervalbetween the distal end faces of both the plungers 16, 16, and aninterval between the other end portions of both the rocker arms 17 n, 17n is expanded so as to match the interval between both the valveelements 12, 12. In contrast, an interval between internal surfaces ofthe intermediate portions of both the rocker arms 17 n, 17 n isnarrowed, so as to control an axial displacement permitted to the tappetroller 9 to a desired magnitude (a minute amount).

In this embodiment, too, there is provided an advantage that the axialdimension of the tappet roller 9 is not necessary to be increased so asto match the interval between the distal end faces of both the plungers16, 16 and the interval between the proximal end faces of both the valveelements 12, 12. The other configuration and function are similar tothose of the ninth embodiment.

The aforesaid advantage that the axial dimension of the tappet roller 9is not necessary to be increased so as to match the interval between thedistal end faces of both the plungers 16, 16 and the interval betweenthe proximal end faces of both the valve elements 12, 12 can be obtainedby other constructions.

As such constructions, for example, a construction as shown in FIG. 24Ais considered in which thickness of a pair of rocker arms 17 o, 17 o areboth made relatively large at intermediate portions of both the rockerarms 17 o, 17 o and are made relatively small at one end portions andthe other end portions thereof, so that an interval between internalsurfaces of both the rocker arms 17 o, 17 o which oppose to each otheris made relatively narrow at the intermediate portions and is maderelatively wide at the one end portions and the other end portions ofboth the rocker arms 17 o, 17 o. Alternatively, as shown in FIG. 24B, aconstruction can also be adopted in which spacers 32, 33 which are bothfitted on a support shaft 7 a are disposed in each of intervals definedbetween internal surfaces of a pair of rocker arms 17 p, 17 p and bothaxial end faces of the tappet roller 9.

Eleventh Embodiment

FIGS. 25 to 27 show an eleventh embodiment of the invention. A camfollower device of this embodiment is built in a valve train of anengine (of an OHC or DOHC type) such as, for example, a three-valveengine, a four-valve engine or a fifth-valve engine in which the numberof at least one of inlet valves and exhaust valves provided per cylinderis made to be two or more. The thus designed cam follower device of theembodiment includes a pair of plate-shaped rocker arms 17 q, 17 q whichare identical to each other in shape and size, a single support shaft 7a and a single tappet roller 9.

Of these components, the pair of plate-shaped rocker arms 17 q, 17 q aredisposed parallel to each other with a predetermined interval (the samepitch as a pitch at which a pair of valve elements 12, 12 are disposed)and are joined together so as to prohibit a relative displacementtherebetween by a connecting portion 38 provided in at least onelocation. In addition, the support shaft 7 a is fixed to one endportions (right end portions in FIGS. 25 to 26) of both the rocker arms17 q, 17 q so as to be extended therebetween. Because of this, a pair ofsupport holes 8 a, 8 a is formed concentric with each other at the oneend portions of both the rocker arms 17 q, 17 q in positions alignedwith each other. In addition, after a hardening treatment by immersionquenching is applied to the whole surface of the support shaft 7 a, byexpanding the interval between the rocker arms 17 q, 17 q, both endportions of the support shaft 7 a are press fitted, respectively, ininsides of both the support holes 8 a, 8 a through openings lying onsides thereof which oppose to each other. In addition, in order toexpand the interval between the rocker arms 17 q, 17 q, angles atconnecting portions between the rocker arms 17 q, 17 q and theconnecting portion 38 are increased (to a magnitude which exceeds 90degrees).

Further, in this embodiment, the relative swing of both the rocker arms17 q, 17 q about the support shaft 7 a is prevented by the connectingportion 38. The tappet roller 9 is supported rotatably on an outercircumferential surface of an intermediate portion of the support shaft7 a via a radial needle bearing 10 (refer to FIG. 3). A pair of throughholes 4, 4 is formed concentric with each other at intermediate portionsof the rocker arms 17 q, 17 q in positions aligned with each other. Apair of projecting portions 18, 18 (pressing portions) is provided onlower surfaces of the other end portions (left end portions in FIGS. 25to 26) of the rocker arms 17 q, 17 q. Distal end faces of theseprojecting portions 18, 18 are each made into a partially cylindricalsurface.

The above mentioned rocker arms 17 q, 17 q are fabricated in thefollowing manner. Firstly, as shown in FIG. 27A, by applying stampingprocess to a single sheet metal, a pair of plate-shaped rocker arms 17q, 17 q which are identical to each other in shape and size are formedso that the pair of plate-shaped rocker arms 17 q, 17 q are madeintegral by a connecting portion 38 provided in at least one location.Thereafter, as shown in FIG. 27B, both end portions of the connectingportion 38 are each bent through 90 degrees until the pair of rockerarms become parallel to each other, whereby the pair of plate-shapedrocker arms 17 q, 17 q are formed which are disposed parallel to eachother with a predetermined interval provided therebetween and areconnected together by the connecting portion 38 which is provided in atleast one location so that relative displacement between the rocker arms17 q, 17 q are disabled. Note that in the process of the bendingprocess, both the end portions of the support shaft 7 a having thetappet roller 9 provided around the circumference of the intermediateportion thereof can also be fitted in the support holes 8 a, 8 a,respectively.

As shown in FIGS. 25 to 26, in an assembling state of the above rockerarms 17 q, 17 q to the valve train of the engine, a rocker shaft 5 as astationary shaft is inserted in the respective through holes 4, 4without looseness and interference therebetween, whereby the swingdisplacement of the rocker arms 17 q, 17 q about the rocker arm shaft 5is enabled. In conjunction with this, an outer circumferential surfaceof the tappet roller 9 is brought into abutment with an outercircumferential surface of a cam 2 which is fixedly provided on acamshaft 1, and the distal end faces of the projecting portions 18, 18are caused to strike individually proximal end faces of the two valveelements 12, 12 (the two inlet valves or the two exhaust valves providedfor the same cylinder). When the engine is running, the rocker arms 17q, 17 q are displaced in a swinging fashion about the rocker arm shaft 5in synchronism with each other as the cam 2 rotates, so as toreciprocate the two valve elements 12, 12 in an axial direction bypressing force exerted by both the projecting portions 18, 18 and springforce produced by a return spring 13 (not shown. Refer to FIGS. 30,34.).

As has been described above, when using the cam follower device of thisembodiment, only by providing the single cam 2 and the single tappetroller 9, the two valve elements 12, 12 can be reciprocatedsimultaneously. Therefore, compared with the case where only theconventional cam follower devices are built in the valve train (theindependent cam follower device is built in each valve element), thenumber of components in the valve train can be reduced. Consequently,the resulting valve train can be made smaller in size (space saving) andlighter in weight and can realize reductions in friction and productioncosts.

In addition, in this embodiment, since the construction is adopted inwhich the interval between the rocker arms 17 q, 17 q can be expanded byincreasing the angles at the bending portions from the connectingportion 38, the end portions of the support shaft 7 a can be pressfitted, respectively, in the pair of support holes 8 a, 8 a withoutdamaging the outer circumferential surface of the intermediate portionof the support shaft 7 a. Thus, an immersion quenching, which can beimplemented inexpensive relative to induction hardening, can be adoptedas a hardening treatment applied to the surface of the support shaft 7a. Consequently, the production costs can be suppressed.

In addition, by forming the support shaft 7 a into a circular tubularshape and providing an oil supply hole at an axially intermediateportion thereof, it also becomes possible to supply oil to the radialneedle bearing 10. Similarly, by forming the rocker arm shaft 5 into acircular tubular shape and providing oil holes at an axiallyintermediate portion of the rocker arm shaft 5 in positions lying ininsides of the through holes 4, 4, a slide contact portion between innercircumferential surfaces of the through holes 4, 4 and the outercircumferential surface of the rocker arm shaft 5 can be lubricated.

Twelfth Embodiment

FIGS. 28 to 29 show a twelfth embodiment of the invention. In thisembodiment, cylindrical portions 39, 39 are formed by burring processwhich is applied to peripheral portions of through holes 4 b, 4 bprovided at intermediate portions of a pair of rocker arms 17 r, 17 r,which are disposed parallel to each other with a predetermined intervaland are connected by a connecting portion 38 in at least one location soas to disable relative displacement. These cylindrical portions 39, 39secure an insertion length of a rocker arm shaft 5 (refer to FIG. 26)into the respective through holes 4 b, 4 b and suppress wear at theswing support portions. Since the configuration and function of otherportions are like to those of the cam follower device illustrated in theeleventh embodiment, the description of like portions will be omittedherein.

Note that, in the invention, the connecting portion which connectsintegrally the pair of rocker arms to each other can be formed on theedges of the rocker arms in positions which cause no problem when beingbuilt in the cam follower device, when the cam follower device isassembled on to the engine and when the cam follower device isincorporated in the engine. However, in consideration of enhancement inperformance of the engine (follow-up properties when the engine isrunning at high revolution speeds) to which the rocker arms areincorporated, the position where the connecting portion is formed isdesirably as close to the through hole into which the rocker arm shaftis inserted as possible. This is because the inertia moment around therocker arm shaft can be suppressed to a smaller level as the connectingportion forming position comes closer to the through hole.

Note that in the respective embodiments that have been describedheretofore, the construction (the single-roller type) is adopted inwhich the single tappet roller is disposed round the support shaft.However, when carrying out the invention, a construction (adouble-roller type) can also be adopted in which two outside diameterside and inside diameter side tappet rollers which are combinedconcentrically and relatively rotatably are disposed around thecircumference of the support shaft.

In addition, although not shown, the construction of the invention canalso be applied to a screw type adjuster system, an HLA system in whichthe cam follower device of the invention is combined with lash adjustersand the like.

This patent application is based on Japanese Patent Application (No.2006-96399) filed on Mar. 31, 2006, Japanese Patent Application (No.2006-238741) filed on Sep. 4, 2006 and Japanese Patent Application (No.2006-282123) filed on Oct. 17, 2006, and the contents thereof areincorporated herein in their entireties by reference.

1. A cam follower device that is built in a valve train of an engine inwhich a number of at least one of inlet valves and exhaust valves whichare to be provided per cylinder is two or more, comprising: a pair ofrocker arms which are disposed parallel to each other with apredetermined interval provided therebetween and have a pair of supportholes which are concentric with each other at one end portions orintermediate portions thereof in positions which are aligned with eachother; a support shaft which is fixed to both the rocker arms so as tobe extended between the rocker arms by fitting both end portions in thesupport holes, respectively; a tappet roller which is supportedrotatably around a periphery of an intermediate portion of the supportshaft, an outer circumferential surface of the tappet roller beingcapable of abutting with an outer circumferential surface of a cam whichis fixed on a camshaft when the cam follower device is built in thevalve train; and a pair of pressing portions which are provided directlyor via a separate member at the other end portions of both the rockerarms, the pair of pressing portions being capable of strikingindividually proximal end faces of two inlet valves or two exhaustvalves when the cam follower device is built in the valve train.
 2. Thecam follower device as set forth in claim 1, wherein the pair of rockerarms is formed separately.
 3. The cam follower device as set forth inclaim 2, wherein the pair of support holes are formed at the one endportions of the pair of rocker arms, and a pair of through holes, intowhich a rocker arm shaft provided in parallel with the camshaft iscapable of being inserted when the cam follower device is built in thevalve train, are formed at the intermediate portions of the rocker armsin positions which are aligned with each other, so as to enable aswinging displacement of both the rocker arms.
 4. The cam followerdevice as set forth in claim 3, wherein an interval between innersurfaces of both the rocker arms which confront each other are maderelatively narrow at the one end portions and relatively wide at theother end portions of both the rocker arms by making thickness of boththe rocker arms relatively large at the one end portions and relativelysmall at the other end portions of both the rocker arms.
 5. The camfollower device as set forth in claim 3, wherein an interval betweeninner surfaces of both the rocker arms which confront each other aremade relatively narrow at the one end portions and relatively wide atthe other end portions of both the rocker arms by providing non-parallelplate portions which are not parallel to the intermediate portions ofboth the rocker arms at portions between the one end portions and theintermediate portions or between the intermediate portions and the otherend portions of both the rocker arms.
 6. The cam follower device as setforth in claim 3, wherein both end portions of a cylindrical sleeve areinwardly fitted and fixed, respectively, in the pair of through holesand the rocker arm shaft is inserted into an inside of the sleeve. 7.The cam follower device as set forth in claim 2, wherein the pair ofsupport holes are formed at the intermediate portions of the pair ofrocker arms, and the one end portions of both the rocker arms have apair of receiving portions which are provided thereon directly or viaseparate members and with which distal end faces of a pair of plungersis capable of being brought into abutment when the cam follower deviceis built in the valve train, so as to enable a swinging displacement ofboth the rocker arms about abutment portions between the receivingportions and the distal end faces of the pair of plungers as fulcrums.8. The cam follower device as set forth in claim 7, wherein an intervalbetween inner surfaces of both the rocker arms which confront each otherare made relatively narrow at the one end portions and relatively wideat the other end portions of both the rocker arms by making thickness ofboth the rocker arms relatively large at the one end portions andrelatively small at the other end portions of both the rocker arms. 9.The cam follower device as set forth in claim 7, wherein an intervalbetween inner surfaces of both the rocker arms which confront each otherare made relatively narrow at the one end portions and relatively wideat the other end portions of both the rocker arms by providingnon-parallel plate portions which are not parallel to the intermediateportions of both the rocker arms at portions between the one endportions and the intermediate portions or between the intermediateportions and the other end portions of both the rocker arms.
 10. The camfollower device as set forth in claim 1, wherein an axial displacementamount allowed to the tappet roller is controlled to a desired magnitudeby disposing spacers which are fitted on the support shaft,respectively, between inner surfaces of both the rocker arms and bothaxial end faces of the tappet roller.
 11. The cam follower device as setforth in claim 1, wherein thickness of portions of both the rocker armswhich need to have a higher strength than that of peripheral areasthereof are larger than thickness of the peripheral areas.
 12. The camfollower device as set forth in claim 2, wherein the pair of rocker armsis each formed by applying stamping process to a single sheet metal. 13.The cam follower device as set forth in claim 1, wherein the pair ofrocker arms is connected together by a connecting portion provided in atleast one location so as to prohibit a relative displacement.
 14. Thecam follower device as set forth in claim 13, wherein the pair ofsupport holes are formed at the one end portions of the pair of rockerarms, and a pair of through holes into which a rocker arm shaft providedin parallel with the camshaft is capable of being inserted when the camfollower device is built in the valve train, are formed at theintermediate portions of the rocker arms in positions which are alignedwith each other, so as to enable a swinging displacement of both therocker arms.
 15. The cam follower device as set forth in claim 13,wherein the pair of rocker arms which are connected together by theconnecting portion provided in at least the one location so as toprohibit a relative displacement are made by applying stamping processand bending process to a single sheet metal.